Could you reasonably merge a lot of the ones that have very few people in them???
Why would you?
They have a minimal government structure. Folks would have to travel further to the county seat when they did need services. One of the big services is is maintenance of county roads. Would the absorbing county provide the same level of maintenance. If there is a major crime, call in the Texas Rangers, and the trial will be in district court.
Exceptions might be Dallam and Hartley, and Potter and (northern) Randall.
Delegate maintenance of the county website to a regional council of governments.
I am talking about ones that have very few people in them. One of them has less than 100. Having fewer counties would make sense as a lot of the infrastructure is redundant.
What sort of infrastructure is redundant?
BTW, Loving County is the fast growing county in the country.
Which county would you merge the small counties with (start with the 8 counties with fewer than 1000 persons).
I'd start with merging Loving, Winkler, and Ward Counties into a Monahans County, with Monahans being the county seat. At 169+7110+10658= 17837 people (2010 census) and 677+841+836=2354 miČ area, it's still fairly small, especially compared to the trans-Pecos counties.
Now for the rest of the sub-1000, since you wanted ideas for all of them.
Borden seems to have most in common with Dawson.
Given the dominance of the King Ranch over both counties, Low population Kenedy should be merged into Kleberg.
While Kent is smaller in population than Stonewall to its east, I'd have the merged county keep the Kent name, but put the county seat in Aspermont.
King has several logical possibilities, but I already merged Stonewall with Kent, and merging with Dickens reduces the number of counties named after Alamo defenders, so merging with Knox, keeping the name of the smaller county and the county seat of the larger, as I did with Kent and Stonewall, seems the best solution here.
McMullen with LaSalle.
Roberts with Hemphill.
As for Terrell, I'd leave it alone for now. The only logical possibility to merge it with is Pecos and both Terrell and Pecos are trans-Pecos counties, which are all large in area. That said, it's down to around one-fourth of its 1950 population, so the merger may need to eventually happen.